Count Submatrices With All Ones LeetCode solution in JavaScript

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/**
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 * @param {number[][]} mat
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 * @return {number}
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 */
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var numSubmat = function (mat) {
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  var m = mat.length;
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  var n = mat[0].length;
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  for (let i = 0; i < m; i++) {
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    for (let j = n - 2; j >= 0; j--) {
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      if (mat[i][j] === 0) continue;
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      mat[i][j] += mat[i][j + 1];
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    }
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  }
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  var sum = 0;
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  for (let i = 0; i < m; i++) {
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    for (let j = 0; j < n; j++) {
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      if (mat[i][j] === 0) continue;
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      var min = mat[i][j];
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      for (let k = i; k < m; k++) {
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        if (mat[k][j] === 0) break;
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        min = Math.min(min, mat[k][j]);
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        sum += min;
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      }
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    }
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  }
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  return sum;
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};